1. Field of Invention
This invention relates to optical devices and, in particular, to optical viewing apparatus having an off-axis direction-of-view suitable for medical examination applications.
2. Discussion of Related Art
Optical systems as components of endoscopic apparatus have been disclosed. For example, Yamasita et al., in U.S. Pat. No. 4,113,354, disclose a single-lens reflex optical system for an endoscope. The disclosed system includes a first prism having a reflecting mirror with a small hole located at a position near the aperture stop of the photographing optical system, a second prism cemented to the first prism, and an observing optical system arranged near the exit surface of the second prism.
Yamasita et al., in U.S. Pat. No. 4,140,364, further disclose a variable field optical system for endoscopes. The optical system has an image guide, an objective, a fixed prism and a rotatable prism, which enables observation over a wide range of varying field.
Yabe, in U.S. Pat. No. 4,757,805, discloses an endoscope. The endoscope has an insertion section as a distal structure in which is disposed an objective optical system to be substantially parallel to the longitudinal axis thereof. A solid-state image sensing device, which has a light receiving surface with an image area is disposed in the distal structure so as to be substantially parallel to a plane which contains the longitudinal axis of the distal structure. An optical element is attached to an end portion of the objective optical system whereby the optical path of light incident on the objective optical system is bent substantially at right angles so that light is guided to the light receiving surface of the image sensing device.
Kikuchi et al., in U.S. Pat. No. 6,558,316, disclose an endoscope optical system including a composition having durability to a sterilization treatment.
Schara et al., in U.S. Pat. No. 6,648,817, disclose an apparatus and method for stereo viewing in variable direction-of-view endoscopy. The variable direction-of-view endoscope has a spherical window symmetric about a symmetry plane sealed to a distal end portion.
Furusawa et al., in U.S. Pat. No. 6,456,769, disclose a fiber bundle and endoscope apparatus. The fiber bundle consists of first optical fibers and second optical fibers. At a distal end of the fiber bundle, the first and second optical fibers are bundled in a square close-packed array or a hexagonal closed-packed array.
Dohi et al., in U.S. Pat. No. 6,626,828, disclose a body cavity-observing apparatus. The body cavity-observing apparatus includes an endoscope with an imaging optical system on the front edge thereof, a prism movably mounted on the forefront of the imaging optical system, and an actuator to drive the prism on a given command signal.
Furusawa et al., in U.S. Pat. No. 6,790,175, further disclose an endoscope system. The endoscope system is provided with a light guide including a plurality of optical paths, and a low-coherent light source that emits a low-coherent light beam. The low-coherent light source is provided with a proximal end side of the light guide. The light beams emitted by the low-coherent light source are incident on the plurality of optical paths. The endoscope system is further provided with an interferometer unit, a driving unit that moves the interferometer unit toward/away from an object, and a signal processing system that generates a tomogram based on signals detected by the light detecting devices.